<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<html>
<head>
<!-- Copyright 1997 The Open Group, All Rights Reserved -->
<title>mq_notify</title>
</head><body bgcolor=white>
<center>
<font size=2>
The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

</font></center><hr size=2 noshade>
<h4><a name = "tag_000_007_742">&nbsp;</a>NAME</h4><blockquote>
mq_notify - notify process that a message is available
(<b>REALTIME</b>)
</blockquote><h4><a name = "tag_000_007_743">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="mqueue.h.html">mqueue.h</a>&gt;

int mq_notify(mqd_t <i>mqdes</i>, const struct sigevent *<i>notification</i>);
</code>
</pre>
</blockquote><h4><a name = "tag_000_007_744">&nbsp;</a>DESCRIPTION</h4><blockquote>
If the argument
<i>notification</i>
is not NULL,
this function registers the calling process to be notified
of message arrival at an empty message queue
associated with the specified message queue descriptor,
<i>mqdes</i>.
The notification specified by the
<i>notification</i>
argument will be sent to the process
when the message queue transitions from empty to non-empty.
At any time,
only one process may be registered for notification by a message queue.
If the calling process or any other process has already registered
for notification of message arrival at the specified message queue,
subsequent attempts to register for that message queue fail.
<p>
If
<i>notification</i>
is NULL and the process is currently registered for notification
by the specified message queue,
the existing registration is removed.
<p>
When the notification is sent to the registered process,
its registration will be removed.
The message queue will then be available for registration.
<p>
If a process has registered for notification of message arrival
at a message queue and some thread is blocked in
<i><a href="mq_receive.html">mq_receive()</a></i>
waiting to receive a message when a message arrives at the queue,
the arriving message satisfies the appropriate
<i><a href="mq_receive.html">mq_receive()</a></i>.
The resulting
behaviour is as if the message queue remains empty,
and no notification is sent.
</blockquote><h4><a name = "tag_000_007_745">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion, the
<i>mq_notify()</i>
function returns a value of zero;
otherwise, the function returns a value of -1 and sets
<i>errno</i>
to indicate the error.
</blockquote><h4><a name = "tag_000_007_746">&nbsp;</a>ERRORS</h4><blockquote>
The 
<i>mq_notify()</i>
function will fail if:
<dl compact>

<dt>[EBADF]<dd>
The
<i>mqdes</i>
argument is not a valid message queue descriptor.

<dt>[EBUSY]<dd>
A process is already registered for notification by the message queue.

<dt>[ENOSYS]<dd>
The function
<i>mq_notify()</i>
is not supported by this implementation.

</dl>
</blockquote><h4><a name = "tag_000_007_747">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_748">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_749">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="mq_open.html">mq_open()</a></i>,
<i><a href="mq_send.html">mq_send()</a></i>,
<i><a href="mqueue.h.html">&lt;mqueue.h&gt;</a></i>,
<i><a href="msgctl.html">msgctl()</a></i>,
<i><a href="msgget.html">msgget()</a></i>,
<i><a href="msgrcv.html">msgrcv()</a></i>,
<i><a href="msgsnd.html">msgsnd()</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)
</blockquote><hr size=2 noshade>
<center><font size=2>
UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]

</font></center><hr size=2 noshade>
</body></html>

